Aggregation by depletion attraction in cultures of bacteria producing exopolysaccharide.

In bacteria, the production of exopolysaccharides--polysaccharides secreted by the cells into their growth medium--is integral to the formation of aggregates and biofilms. These exopolysaccharides often form part of a matrix that holds the cells together. Investigating the bacterium Sinorhizobium meliloti, we found that a mutant that overproduces the exopolysaccharide succinoglycan showed enhanced aggregation, resulting in phase separation of the cultures.

Beta-AMYLASE4, a noncatalytic protein required for starch breakdown, acts upstream of three active beta-amylases in Arabidopsis chloroplasts.

This work investigated the roles of beta-amylases in the breakdown of leaf starch. Of the nine beta-amylase (BAM)-like proteins encoded in the Arabidopsis thaliana genome, at least four (BAM1, -2, -3, and -4) are chloroplastic. When expressed as recombinant proteins in Escherichia coli, BAM1, BAM2, and BAM3 had measurable beta-amylase activity but BAM4 did not.